Electric wave sampling device



p l 21, 1953 T. s. SAAD 2,636,082

' ELECTRIC WAVE SAMPLING DEVICE Filed May 29, 1948 3 Sheets$heet l 1 M/I/EA/ 70/? U/t'ODQ/ PE 5. 5/9/90 April 21, 1953 'r. s. SAAD ELECTRIC WAVE SAMPLING DEVICE s Sheets-Sheet 2 Filed May 29, 1948 9% a %ji 197' 05y April 21, 1953 'r. s. SAAD 2,636,082

ELECTRIC WAVE SAMPLING DEVICE Filed May 29, 1948 3 Sheets-Sheet C5 Patented Apr. 21, 1953 2,53 2 ELECTRIG WAVE SAMPLING nov ce Theodore S. Saad, West Roxbury, Mass, assignor to sax thew Manuf tu ing Company, a cor- Application May 29, 1948, Serial No, 30,041

2} Claims. 1

This invention relates in general to electrical equipm t for pa n the lta e mea 95 of two guided periodic electric waves of the same frequency, and in particular to an arrangement for comparing the voltage magnitudes of two such waves which are traveling in a single transmis sion line.

It is an object of the invention to provide a means for simultaneously comparing the voltage magnitudes of two waves of the same irequency which are traveling in opp site directions in a waveguide, coaxial line, or the like.

It is another object of the invention to provide such means which is useful over a wide band of frequencies.

It is still another object to providesucn means which is convenient to employ and can be inserted in a transmission line system with little or no effect upon the normal operation of the system.

It is a further object of the invention to provide such a means which can be constructed with ordinary techniques and of readily ayailablecome ponent parts.

From another point of view, it is an object of this invention to provide a means for automatically and continuously indicating the standing wave ratio of a guided wave transmission system.

The foregoing and other objects and features of the invention will become apparent from the description or a particular embodiment thereof that follows. The description refers to the accoinpanying drawing wherein:

Fig. 1 is an isometric view of an embodiment of the invention;

Fig. 2 is a side View of Fig. 1;

Fig. 3 is a sectional view on line 3-3 of Fig. 2;

Fig. 4 is a sectional view on line 4-4 of Flig. 3;

ig. 5 is a ble di ra l us rat g a i c i c l mpi yine he de i e shot e11 F l:

r Fig. 6 illustrates the nature of the traveling w v s tha a ob e e i a? d vice an. tdF

he 7 i u a einvention; and i .8 u a es still an ther em gimtai at the invention.

Referring now-to Figs. 1 to 4, inclusive, a I waueguide ill is provided ith a .longitugli lly cited narrow .slot a in the lower .wi'de wall ll th g m class t we o the na ro 1 .1" and a i svej e ly e fli pe Wide ca t anot er sent men .112. 6

11w s wall- Th se slot are sampling the waves travelin in the main wave;

guide Ill, and they do not seriously disturb he of energy. The centers of the two slots a.

lie in'a' common plane (not shown) which" transverse to the longitudinal axis of he wave guide as is apparent from Fig. i.' The common plane of the slot centers is'equidistant from I arbitrarily chosen terminals l and? in tlile'e of the main waveguide 'l'll. a f rst auxiliary rectangular waveguide 14 is electrically coupled at 'its'upper wide wall. [5 to the main waveguide lll'throughs'lot (tin such fashion that slotu is transversely disposed tosaid upper wide wall it, a'fdis centered on the lo a tudinal center line thereof. The two ends of f rst auxiliary waveguide hi are denominated er; inals 3 and 4, e pe i ely T s Yt'rhiifi ls may he equidistant from the center of slot "mas is shown in Fig. 53, if desired. The describeddis; position f slot a with respect to the first aui'i T Waveguide .14 is acq i b d q is he li l ia wa e d endic ar y to t main Wav guide ill and connecting the two waveguides to,- gether at their upper and lower wide walls iii and II, respectively. The connection is conven iently made by removing a portion ,ofone Wide wall so that the wide wall of one of the two wave,- guides functions as a common wide wall .section between them. Slot a is then conveniently out in this common section. The seams between the two waveguides are then electrically connected together, as by soldering. In the embodiment illustrated in Figs. 1 to 4, inclusive, the upper wide wall [5 of the auxiliary waveguide [4 base. portion removed (as shown in Fig. 3), and "the corresponding portion of the lower wide wall of the main waveguide Hi provides'a common wide wall section between the two waveguides.

A second auxiliary rectangular'w aveguide I6 is electrically coupled at its lower widewall ll to t e mai wave uide ll h u ,s lot fi i .s h fashion that SlQt b islongitudinallydispsdtb said lower wide wall J7, and is positioned cry close to a side wall 18 thereof. The ends of the second auxiliary waveguide it are denominated terminals 5 and 6, respectively, andmay als be equidistant from the center of slot b desired, as shown in Fig. 3. The described disposition of slot h with respect to the second auxiliary aveguide I5 is acquired similar fashiontas the disposition of slot at withrespectto tr" first tuitiiary Waveguide 4i i owe wi e tal I? of he seeped uiting w e uide "Wh t a ortion r5,

. 3 moved, and a portion of the upper wide wall It of the main waveguide it provides a common wide wall section, in which a slot 1) is out, as is apparent in Fig. 3.

One terminal of each of the auxiliary waveguides is provided with a non-reflective or matched termination 28. As shown in Fig. 3, these terminations are in terminals d and t, and have a wedge shape. The terminations may be made of any suitable resistive material. For example, a body of Bakelite coated with colloidal graphite, commonly known as aquadag," or a long tapering wedge of hardwood, is a satisfactory termination.

The two traveling waves under observation ccour in the main waveguide it, and, as will be developed below, two voltages appear at terminals 3 and 5 which are, respectively, proportional to the sum and the difference of the voltages of the observed waves at some arbitrary point in the main waveguide. While there are many situations in which it is desired to compare the volt ages of two waves of like frequency, one common situation is illustrated in Fig. 5. This is the situation wherein a source of radio frequency power 2|, for example, a magnetron, is connected to a load 22, such as an antenna, through a transmission line, for example, the waveguide 23, and it is desired to know conveniently and continuously what is the standing wave ratio in the transmission line. The standing wave ratio is a function of the portion of the incident power that is reflected from the load, and hence not used by it. The standing wave is a result of the combination of the waves that are incident upon and the waves that are reflected from the load. There are, therefore, two waves of like frequency traveling in opposite directions the main transmission waveguide 23. The main waveguide it of the device of the invention is inserted in the transmission waveguide 23 with terminal i toward the R. F. source, so that these two traveling Waves pass through it. A matched attenuator pad 2 which may be a wave transmissive pad of resistive material, is inserted between terminal 5 and the R. F. source 2 l, to prevent noticeable rerefiection, from the source, of waves that have already been reflected from the load. The transmission waveguide 23 is provided with a section of variable length 25, for a purpose to be explained below.

Consider now the electrical nature of the device shown in Figs. 1 to 4. The waves in the main waveguide l8 are waves in the fundamental, or TEOl, mode for rectangular waveguides. As is well known, it is characteristic of such waves that the voltage difference occurs between the Wide walls of the waveguide and is maximum between their center lines. The voltage gradient varies periodically along the longitudinal axis that exists between these center lines. As shown in Fig. 6, where the arrows on the waveguide Walls depict an instantaneous current flow pattern, current flows both axially and transversely to the axis in the wide walls of the waveguide. The longitudinally directed slot a is excited by transverse current flow, while the transversely directed slot 1) is excited by axial current flow. Slot a is said to be in shunt with the main waveguide it, and slot b in series therewith. Since axial current flow is maximum at the center line of the wide wall, the series slot b is located on the center line. Similarly, the shunt slot at is located near a side wall because transverse current flow is greatest there. The two slots are both made so thin 4 that a field in one does not excite a field in the other, for all practical purposes.

Considering now the shunt slot 11, this slot couples a small amount of energy from the main waveguide id into the first or lower auxiliary waveguide l4. While slot at is in shunt with the main waveguide 18, it is in series with the aux iliary waveguide i4. At any one instant of transverse current fiow across slot a there is set up a voltage gradient between the two long edges of the slot which excites a field in the slot. This field propagates antisymmetrical Waves, that is, waves which are elec 'ical degrees out of phase with each other, in opposite directions in the auxiliary waveguide i i. Recalling now that terminals i and 2 are equidistant from the center of slot at, it is apparent from Fig. 6 that, if symmetrical voltage waves of like frequency are impressed on terminals i and 2, respectively, they will both excite slot a in the same phase. This is so because the direction of the current that excites slot at is the same for both Waves. Therefore the voltage that is available at either of the terminals 3 and s of the first auxiliary waveguide is is proportional to the sum of the voltages at terminals l and 2 when they are symmetrical, or in the same phase.

Considering now the series slot 12, this slot couples a small amount of energy from the main waveguide it into the second or upper auxiliary waveguide 55. While slot b is in series with the main waveguide H3, it is in shunt with the second auxiliary waveguide i6. At any instant of lon tudinal current flow across slot 22, there is set up a voltage gradient across the slot which excites a field in the slot, and this field in turn propagates symmetrical waves in opposite directions in the second auxiliary waveguide l6. It is apparent from Fig. 6 that, when symmetrical voltage waves are incident upon terminals l and 2, respectively, the longitudinal current flows across slot b are in opposition, and tend therefore to reduce the voltage gradient across the slot, so that the field set up in the slot is a function of the difference between the two voltages. Thus the voltages available at the terminals 5 and 8 of the uppe auxiliary waveguide iii are proportional to the difference between symmetrical voltages incident at terminals 1 and 2.

From the foregoing discussion, it can be seen that, if antisymmetrical voltage waves are incident upon terminals I and 2, respectively, the voltages available at terminals 3 and 4 are proportional to their difference, while the voltages available at terminals 5 and 6 are proportional to their sum, respectively.

Referring again to Fig. 5, the voltage that is incident upon terminal I is proportional to the power applied to the load 22, while the voltage incident upon terminal 2 is proportional to the power reflected from the load 22. With terminals 4 and 6 closed by the non-reflective terminations 20, the voltages available at terminals 3 and 5 are compared, for example, in a ratio. meter. If there is no reflected voltage, the two slots a and b are equally excited, and the sum voltage and the difference voltage available at terminals 3 and 5 are equal. This then represents a standing wave ratio of unity, which is the ideal case. Usually, however, the reflected voltage value lies somewhere between zero and the value of the incident voltage, so that the ratio of the sum to the difference of the two is a fraction greater than one. This fraction is pro-' portional to the standing wave ratio.

escapesv It "will be recalled that the voltages at terminals I and 2 should be symmetrical or antisymmetrical. This is desirable because the peaks of the incidentand reflected voltage waves should be compared to provide a true measure of the standing wave ratio, or, in terms of the resultant standing wave itself, a peak and a trough thereof should be compared. However, there is no assurance that the reflected wave will arrive at terminal 2 in the desired phase with respect to the incident voltage at terminal I; Hence the variable length line section 25 is included. In practice, one .needs only to vary the electrical length of the variable line section :25 until the ratio between the voltages available at terminals 3 and is a maximum to determine the standing wave ratio in the transmission line 23. Any form of phase shifter, preferably .as near refiectionless as possible, is suitable for this purpose.

'In the foregoing explanation of the operation of the invention, it has been assumedthat neither of the fields in the slots excites a field in the other slot, and that all the terminals are so well matched that there are no reflections from any of them to excite spurious fields in the slots. To minimize interaction of the slots with the quantities being measured, the slots are made as thin as is practically possible. This is feasible because the slots merely sample the voltages that are present in the main wave guide l0,:and do not couple substantial power. For example, the power level of coupled energy is about .20 db. below that of the source power in the main wave guide. Calculations on the models made .and used shave shown that the error "in standing wave ratio measurements .due tosuchinteraction is at most about one-half of one percent of the :true value. Matching of the terminals is .accomplished with proper care at each terminal; for example, the pad 24 in Fig. .5 prevents re-rreflection of reflected energy that enters the .device at terminal 2, while the terminations illare for :all practical'purposes reflectionless.

When the unused terminals 4 "and .6 of the auxiliary waveguides IR and I6, respectively, are terminated in the non-reflective terminations "2.0, these terminals can be :any convenient distance from the slots a or ib,'rtespectively. .Itwill-be'appreciated that all the :so-called terminals, 1 and 2, '3 and 4, and :5 and 6, are merely :reference points which are chosen to facilitate an understanding .of the invention. .In actual practice, for example, 'as in Fig. .5, a variable length line section like section 25 will yield the desired operation with respect to terminals I and 2, and the measuring terminals3 Land 5 can be any iconvenient distance from'the slots.

The device shown in Figs. l to 4, inclusive, :is not sensitive to changes :inzthe frequency of the voltages being measured, butratheris operative throughout'the band of frequencies that can be transmitted through the waveguides. The reasonifor this is that the slots 3a and 12, being placed with their centers in the same transverse plane in the main waveguide Jill, actually couple currents which are at all times 90 electrical degrees apart for all frequencies :of the same mode of transmission. Therefore, it may be said that from this point of view these slots are 90-electrical degrees apart. This is apparent from ,Fig. 6, where, for the s-akeof explanation, the two slots are shown in the same wall of the waveguide. At the instant when .thecurrentflow acrossslot aisat amaximum valuathe currentfiow across slot b is at a minimum value. 90 electrical dewaveguides.

tion of a wavelength only at a particular :fre-

quency. Then changes in frequency would alter the relative phase of the two output voltages. For the purposes of measuring standing .wave power, this feature permits the simultaneous comparison of 'peak and trough values of the standing wave power over the complete bandof frequencies that are transmissible in the wave.-

uide.

It is now evident that the invention provides a means for comparing two voltage waves of the same frequency and traveling in opposite directions in a waveguide, wherein two identical sampling devices located in a common plane transverse to the path of travel sample the waves at points which are :always 90 electrical degrees apart and provide voltages which are, respectively, proportional to the sum and the difference of the voltages of the sampled waves. In the embodiment described :above, the sampling is .by way of slots a and b, which serve to transfer or couple small portions of energy from the main waveguide to one or another of the auxiliary 'The invention is not limited to the details of this embodiment, however, for it can i be practiced with other forms :of energy coupling or sampling devices, such as probes, coupling loops, and the like. In addition, the invention can be practiced with coaxial lines as well :as waveguides.

Referring "now to Fig. 7, an embodiment of the invention is shown wherein three rectangular waveguides 30, 31, and 32 are coupled together through common wide walls 33 and :34. "The intermediate waveguide is the main waveguide, and it shares a separate wide wall .33 or 34 with each of the auxiliary waveguides 3i and 32, respectively. The main waveguide 36] has a probe 35 disposed in the upper wide wall 33 for coupling with "the electrostatic field, and a loop 36 disposed in "the lower wide wall 31 for coupling with the electromagnetic held of thefundamental ,mode waves. The loop 36 is shielded by tubes .3! and 38 at both ends, and only a region which is substantially parallel to the axis of the main waveguide is left exposed for ecupling with only the magnetic field, and not with the electrostatic field. The shielding tubes '3"! and 33 are mounted directly on the lowerwide wall .34 and electrically grounded thereon. The loop is connected at one end o he same wall inside .ones'h'ielding .tube31 and pierces thewall at the other end '39 through a hole 40 bored in the common wall .34 concentric with the base of the other shielding tube .38. The other "end 39 of the loop {3B extends into thelower auxiliary waveguide 32 to provide a probe for exciting electric waves therein,.,so that the loop 35. and'its probe .39 serve to sample the wave fields in the main waveguide 30 and set up waves in the auxiliary waveguideinresponse thereto. The probe 35 in the upper wide wall 33 passes through a holeill in .the wall and is ,connected .to alloop 4 2 which cooperates with the upper auxiliary wavethe main waveguide the probe and loop are disposed with their centers in the same transverse plane. Since one'couples with the electrostatic field and the other with the electromagnetic field, they are effectively 90 electrical degrees apart in the main waveguide 36 for all frequencies.

field, while the probe 35 couples only with the electrostatic field, the two coupling devices do not affect each other. The loops 36 and 42 are excited by or set up antisymmetric waves, while the probes 35 and 39 are'excited by or set up symmetric waves. The main waveguide terminals I and 2 are equidistant from the plane of the probe 35 and loop 3'5, while if desired terminals 3 and 4 may be equidistant from the probe 39 in the lower auxiliary waveguide 32,v and terminals 5 and 6 may be equidistant from the loop 42 in the upper auxiliary waveguide 3!. While in the embodiment of Fig. 1 accurate performance is secured by employing thin slots (a and 1)), here the loops 36 and 42 should be made small and the probes should be accurately located. The three waveguides 3d, 3! and 32 may be disposed mutually perpendicularly as in Fig. 1, if desired, by relative rotation of any two of the waveguides around the axis of the probe 35 or 39 in one of them.

Referring now to Fig. 8, the invention is there shown as practiced with coaxial lines. A main coaxial line 53 and two auxiliary coaxial lines 5| and 52 are coupled together through two thin slots 53 and 54. The slots are cut in the outer tube 55 of the main line 50, at diametrically opposed points and centered in a common transverse plane. One slot 53 is circumferentially directed, and the other 54 is axially directed. The auxiliary lines 5| and 52 are conveniently connected to the main line by removing a portion of the outer tube of each auxiliary line so that a portion of the outer tube 55 of the main line, containing one of the slots, fits therein, and electrically and mechanically connecting each auxiliary line to the main line at one of these 1 tions. The auxiliary lines are attached perpendicularly to the main line and parallel to each other, as are the waveguides in the embodiment of Fig. l. A first probe 53 extends into the main line 50 from the wall near a long edge of the axially directed slot 54, and a second similar probe 5'! extends into the upper auxiliary line 5| from the wall near a long edge of the circumferentially directed slot 53'. The first probe 56 lies in the aforementioned common transverse plane occupied by the centers of the two slots.

In operation, the upper slot 53 is excited by longitudinal current flow in the inner skin of the outer tube 55 of the main line 59, while the lower slot 54 is excited through the first probe 56 by the electrostatic field between the inner conductor 58 and the outer tube 55. The two slots are thus excited 30 electrical degrees apart for all frequencies that are carried in the main line. The upper slot 53 in turn excites its probe 51 in the upper auxiliary line 5|, which sets up .Since the loop 36 is shielded from the electrical and couples only with the magnetic symmetrical voltages which travel in opposite directions toward the terminals 5 and 6. The lower slot 54, which is effectively circumferentially directed with respect to the lower auxiliary line 52, sets up antisymmetric voltages in that line which travel in opposite directions toward the terminals 3 and 4 thereof.

. It will be readily appreciated by those skilled in the art that there are many other specific arrangements that suit the purposes of the present invention. No attempt is made here to exhaust all the possibilities that come to mind.

Different arrangements may employ slots, probes, loops, and combinations of these and even other devices as sampling or coupling elements between two transmission lines. Accordingly, the term sampling device that is used in the following claims is intended to include all these various forms. The invention is not limited'to the details of any particular form of sampling element, nor is it limited to other details of any of the particular embodiments shown herein by way of illustration. Therefore it is intended that the claims that follow shall be limited only by the prior-arti I claim:

1. An electric. wave transmission line device comprising: a main rectangular waveguide; a first wide wall of said wave guide having only a single transversely directed slot centered substantially on the center line in said first wide wall; the second wide wall of said waveguide having only a single longitudinally directed slot near a side edge in said second wide wall; said slots being substantially ninety electrical degrees apart in said main waveguide; and first and second auxiliary waveguides coupled to said main waveguide, one through each of said slots, respectively.

2. An electric wave transmission line device comprising; a main rectangular waveguide; a first wide wall of said waveguide having only a single transversely directed slot centered substantially on the center line insaid first wide wall; the second wide wall of said waveguide having only a single longitudinally directed slot near a side edge in said second wide wall; said slotsbeing centered in a common plane transverse to the longitudinal axis of said main waveguide; and first and second auxiliary waveguides coupled to said main waveguide one through each of said slots, respectively.

3. An electric wave transmission line device comprising: a main rectangular waveguide; a first wide wall of said wave guide having only a single transversely directed slot centered substantially on the center line in said first wide Wall; the second wide wall of said waveguide having only a single longitudinally directed slot near a side edge in said second wide wall; saidslots being substantially ninety electrical degrees apart in said main waveguide; and first and second auxiliary rectangular waveguides each coupled at a wide wall to said main waveguide through one of said slots, respectively.

4; An electric wave transmission line device comprising: a main rectangular waveguide; a first wide wall of said waveguide having only a single transversely directed slot centered substantially on the center line in said first wide wall; the second wide wall of said waveguide having only a single longitudinally directed slot near a side edge in said second wide wall; said slots being substantially ninety electrical degrees apart insaid main waveguide; and first and sec- 0nd auxiliary rectangular waveguides each coupled at a wide wall to said main waveguide through one of said slots, respectively, each of said auxiliary waveguides having its longitudinal ,axis directed perpendicularly to that of said main waveguide, the first auxiliary waveguide having said transversely directed slot located longitudinally in its coupled wide wall between the longitudinal center line and longitudinal edge thereof, and the second auxiliary waveguide having said longitudinally directed slot located transversely in its coupled wide wall and centered substantially on the longitudinal center line thereof.

5.. An electric wave transmission line device comprising: a main rectangular waveguide; a first wide wall of. said Waveguide having only a single transversely directed slot centered substantially on the center line in said first wide wall; the second wide wall of said waveguide having only a single longitudinally directed slot near a side edge in said second wide wall; said slots being substantially ninety electrical degrees apart in said main waveguide; first and second auxiliary waveguide sections each coupled at a point intermediate its ends to said main wave- 1 guide through one of said slots, respectively.

6. An electric wave transmission line device comprising: a main rectangular waveguide; a first wide wall of said waveguide having only a single transversely directed slot centered substantially on the center line in said first wide wall; the second wide wall of said waveguide having only a single longitudinally directed slot near a side edge in said second wide wall; said slots being substantially ninety electrical degrees apart in said main waveguide; first and second auxiliary waveguide sections each coupled at a point intermediate its ends to said main waveguide through one of said slots, respectively; and a substantially refiectionless termination in one end of each auxiliary waveguide.

7. An electric wave transmission line device comprising: a main and first and. second auxiliary rectangular waveguides, said main wave guide having a different wide wall in common With each of said auxiliary Waveguides, and said auxiliary waveguides being parallelto each other and perpendicular to said main waveguide; the

wall in common with said first auxiliary waveguide having a first single elongated slot only waveguide and near a side wall of the auxiliary waveguide; and the wall in common with said second auxiliary waveguide having a second single elongated slot only therein, said second slot being directed parallel to said axis of said first waveguide and perpendicular to the axis of the auxiliary waveguide, and centered near a side wall of said main waveguide and substantially on the center line of the auxiliary waveguide, said slots being substantially ninety electrical de grees apart in said main waveguide.

8. An electric wave transmission line device comprising: a, main and first and second auxiliary rectangular waveguides, said main wave guide having a dififerent wide wall in common with each of said auxiliary waveguides, and said auxiliary waveguides being parallel to each other and perpendicular to said main waveguide, the wall in common with said first auxiliary waveguide having a first single elongated slot only therein, said slot being directed perpendicularly to the axis of said main waveguide and parallel to the axis of the auxiliary waveguide, and centered substantially on the center line of the main waveguide and near a side wall of the auxiliary waveguide; and the wall in common with said second auxiliary waveguide having a second single elongated slot only therein, said second slot being directed parallel to said axis of said first waveguide and perpendicular to the axis of the auxiliary waveguide, and centered near a side wall of said main waveguide and substan tially on the center line of the auxiliary waveguide; said slots being centered in a common plane transverse to said axis of said main waveguide.

9. An electric wave transmission line device comprising: a main and first and second auxiliary rectangular waveguides, said main waveguide having a different wide wall in common with each of said auxiliary waveguides, a first probe for coupling with the electrostatic field in said main waveguide, a first loop for coupling with the magnetic field in the first auxiliary waveguide, said probe and loop being electrically connected together through the wall in common with said first auxiliary waveguide; a second loop for coupling with the magnetic field in said main waveguide, a second probe for coupling with the electrostatic field in said second auxiliary waveguide, said second probe and loop being electrically connected together through the wall in common with said second auxiliary waveguide; the first probe and second loop being eifectively centered in a common plane transverse to the longitudinal aXis of the main waveguide; and means shielding each loop from the electrostatic field in its waveguide.

10. An electric wave transmission line device comprising: a main and first and second auxiliary rectangular waveguides, said main waveguide having a different wide wall in common with each of said auxiliary waveguides, a first probe for coupling with the electrostatic field in said main waveguide, a first loop for coupling with the magnetic field in the first auxiliary waveguide, said probe and loop being electrically connected together through the wall in common with said first auxiliary waveguide; a second loop for coupling with the magnetic field in said main waveguide, a second probe for coupling with the electrostatic field in said second auxiliary waveguide, said second probe and loop being electrically connected together through the wall in common with said second auxiliary waveguide; the first-probe and second loop being 9f fectively centered in a common plane transverse to the longitudinal axis of the main waveguide.

11; An electric wave transmission line device comprising: a main and first and second auxiliary coaxial lines, said main line having a different portion of its outer conductor in common with each of the auxiliary lines, the auxiliary lines being parallel to each other and perpendicular to the main line; a first coupling slot in the common wall portion between the main and. first lines, disposed transversely to the axis of the main and parallel to the axis of the first lines; a first electrostatic coupling probe projecting into the first line from the wall material adjacent a long edge of said first slot; a second coupling slot in the common wall portion between the main and second lines, disposed parallel to the axis of the main and transversely to the axis of the second lines; and a second electrostatic coupling probe projecting into the main line from the wall material adjacent a long edge of said second slot, the centers of the two slots lying in a common plane transverse to the axis of the mainline.

12. An electric wave transmission line device comprising: a main and first and second auxiliary coaxial lines, said main line having a different portion of its outer conductor in common with each of the auxiliary lines, the auxiliary lines being parallel to each other and perpendicular to the main line; a first coupling slot in the common wall portion between the main and first line's, disposed transversely to the axis of the main and parallel to the axis of the first lines; a first electrostatic coupling probe projecting into the first line from the wall material adjacent a long edge of said first slot; a second coupling slot in the common Wall portion between the main and second lines, disposed parallel to the axis of the main and transversely to the axis of the second lines; and a second electrostatic coupling probe projecting into the main line from the wall material adjacent a long edge of said second slot; the center of the two slots and of said second probe all lying in a common plane transverse to the axis of the main line.

13. An electric wave transmission line device comprising, a main transmission line having a field-enclosing conductor, first and second wave sampling devices in said conductor, located at separate points on opposite sides of the longitudinal axis of said conductor, said devices being constructed and arranged to couple with the electrostatic and the electromagnetic field, respectively, of waves in said line, said devices being disposed in locations where the instantaneous phase difference between said fields is substantially ninety electrical degrees, said sampling devices being the only energy passages through said conductors, and two auxiliary transmission lines, each electrically coupled to one of said sampling devices, respectively.

14. An electric wave transmission line device electrostatic and the electromagnetic fields, re

spectively, of waves in said line, said devices being located in a common plane transverse to the direction of wave travel in said line, said sampling devices being the only energy passages through said conductor, and two auxiliary transmission lines, each electrically coupled to one of said sampling devices, respectively.

15. An electric wave transmission line device comprising, a main transmission line having a field-enclosing conductor, first and second coupling slots in said conductor, said slots being located at separate points on opposite sides of the longitudinal axis of said conductor, said first slot being transversely disposed and said second slot being longitudinally disposed, said slots being arranged to couple in shunt and in series, respectively, with waves in said line, said slots being located at points where the fields influencing them are substantially ninety electrical degrees apart in instantaneous phase, said slots being the only passages through said conductor, and first and second auxiliary transmission lines coupled to said main line, one through each of said slots, respectively.

16. An electric wave transmission line device comprising, a main transmission line having a. field-enclosing conductor, first and second coupling slots in said conductor, said slots being located at separate points on opposite sides of the longitudinal axis of said conductor, said first slot being transversely disposed and said second slot being longitudinally disposed, said slots being arranged to couple in shunt and in series, respectively, with waves in said line, said slots being centered in a common plane transverse to the direction of wave travel in said line, said slots being the only passages through said conductor, and first and second auxiliary transmission lines coupled to said main line, one through each of said slots, respectively.

17. An electric wave transmission line device comprising a main rectangular waveguide having its first wide wall pierced by only a transversely directed slot centered substantially on the longitudinal center line of said first wall and its second wide wall pierced by only a longitudinally directed slot located between the longitudinal center line and a longitudinal edge of said second wall, said slots being spaced along the longitudinal axis of said waveguide substantially ninety electrical degrees at the operating frequency, and separate circuit means coupled to each of said slots.

18. An electric wave transmission line device comprising a rectangular waveguide having its first wide wall pierced by only a transversely directed slot centered substantially on the longitudinal center line of said first wall and its second wide wall pierced by only a longitudinally directed slot located between the longitudinal center line and a longitudinal edge of said second wall, said slots being centered substantially in a common plane perpendicular to the longitudinal axis of said waveguide, and separate circuit means coupled to each of said slots.

19. An electric wave transmission line device comprising a main transmission line, first and second electric wave sampling devices electrically coupled to said line at first and second separate regions, respectively, which regions lie in a common plane transverse to the direction of wave propagation in said line and are loci of electric wave manifestations having an instantaneous phase difference equal to one-quarter period, a first auxiliary transmission line electrically coupled at a point intermediate its ends to said first device in a fashion to propagate coupled energy in like phase toward both of its ends, and a second auxiliary transmission line electrically coupled at a point intermediate its ends to said second device in a fashion to propagate coupled energy in mutually opposite phases toward both of its ends.

20. A transmission line device according to claim 19 including a substantially nonrefiective termination in one end of each of said auxiliary transmission lines.

21. In an electric wave system wherein a generator of electric waves is connected through a transmission line to a load, apparatus for indicating the standing wave ratio in said line comprising a main transmission line section, first and second electric wave sampling devices electrically coupled to said section at first and sec ond separate regions, respectively, which regions lie in a common plane transverse to the direction of wave propagation in said section and are loci of electric wave manifestations having an instantaneous phase difierence equal to one-quarter period, a first auxiliary transmission line 3 electrically coupled at a point intermediate its ends to said first device in a, fashion to propagate coupled energy in like phase toward both of its ends, a second auxiliary transmission line electrically coupled at a point intermediate its ends to said second device in a fashion to propagate coupled energy in mutually opposite phases toward both of its ends, said main section being inserted in said transmission line, and means in said transmission line for adjusting the symmetry of the waves therein with respect to said sampling devices.

THEODORE S. SAAD.

References Cited in the file of this patent UNITED STATES PATENTS Number 14 Number Name Date 2,423,390 Korman July 1, 1947 2,423,416 Sontheimer July 1, 1947 2,445,348 Ford July 20, 1948 2,445,896 Tyrrell July 27, 1948 2,473,274 Bradley June 14, 1949 OTHER REFERENCES Publication II Institution of Electrical Engi- 10 neers, Journal PT. IIIA March-May 1946. Vol.

15 Institute of Radio Engineers, vol. 36, No. 1, January 1948. Copy in I'll-95.23. 

